1. Field of the Invention
This present invention relates to a Multi Chip Package (MCP) type memory system and a replacement method of a replacing a defect therein. For example, the present invention can be used in a computer system, a memory card system, or a mobile phone system that is required to downsize.
2. Description of the Related Art
A recent computer system can be connected to a memory system that comprises of plural kinds of memory integrated circuits that are used as an external memory. When the memory system is used in the computer system (for instance, a mobile terminal), the memory system is strongly required to downsize. And also, recently the Multi Chip Package (MCP) type memory system that includes a plurality of memory chips in a single package is becoming used.
FIG. 10 shows the schematic diagram of the Multi Chip Package (MCP) type memory system. A plurality of memory chips 100 in the Multi Chip Package (MCP) type memory system are commonly connected to each other via a data line 102. The plurality of the memory chips 100 are commonly connected to each other via a control line 103. And also, each of the plurality of the memory chips 100 is connected to a chip select line 104 that supplies a chip select signal from an outside of the Multi Chip Package (MCP) type memory system.
Each of the plurality of the memory chips 100 includes a memory cell region 105, a redundant memory cell region 106 to replace a defect (at least one of a defect memory cell, a defect column line, and a defect world line) in the memory cell region 105, a laser blow type fuse circuit 107 to memorize information regarding the defect, an address decoder, and an I/O circuit.
FIG. 11 schematically shows how to replace a defect region in the memory cell region 105 with the redundant memory cell region 106. When the defect region is found in the memory cell region 105 at a test step to be performed before a packaging step, an address corresponding to the defect region is stored in the laser blow type fuse circuit 107. After that, when the address corresponding to the defect region is selected, non-defect region in the redundant memory cell region is selected, instead of selecting the defect region in the memory cell region 105, thereby replacing the defect region in the memory cell region 105 with the non-defect region in the redundant memory cell region 106. This technique is widely and usually used to replace the defect region with the non-defect region.
By the way, the Multi Chip Package (MCP) type memory system includes a plurality of the memory chips in a single package. Therefore, when the only one of the plurality of the memory chips is defect, even if the others are not defects, the Multi Chip Package (MCP) type memory system itself can not be used. Therefore, productivity rate of the Multi Chip Package (MCP) type memory system is determined by multiplications of productivity rates of all memory chips in the single package, thereby inevitably resulting in much lower productivity rate of the Multi Chip Package (MCP) type memory system than that of the single memory chip.
Conventionally, in order to make the productivity of the Multi Chip Package (MCP) type memory system higher, there is no effective method other than making productivity of all of the each memory chips higher. And also, it was very difficult to make the productivity of all memory chips each of which has different function greater.
A Japanese patent laid open kokai 2003-59288 shows a Multi Chip Package (MCP) type memory system that includes a dedicated line to serially transfer a redundant data among memory chips in order to replace a defect region after incorporating a plurality of memory chips in the Multi Chip Package (MCP) type memory system. However, it is practically difficult to use the technique stated in the Japanese patent laid open kokai 2003-59288 due to a high costs and an unstable operation of the MCP type memory system.